In general, perfluoropolyether-containing compounds have water and oil repellency, chemical resistance, lubricity, parting properties and anti-staining properties because of their very low surface energy. For the effective utilization of such properties, these compounds are widely used in the industry as water/oil repellent anti-staining agents for paper and fibers, lubricants in magnetic recording media, oil repellants in precision machines, parting agents, cosmetics, and protective coatings.
However, the perfluoropolyether-containing compounds also have such properties as non-tackiness and non-adhesion to other substrates. They are applicable to the substrate surface, but cannot form a coating firmly bonded to the substrate.
Silane coupling agents are well known as the means for establishing a firm bond between a substrate surface such as glass or fabric and an organic compound. The silane coupling agent has an organic functional group and a reactive silyl group (typically alkoxysilyl group) in a molecule. The alkoxysilyl group undergoes self-condensation reaction with air-borne moisture, converting to a siloxane to form a coating. At the same time, the silane coupling agent forms chemical and physical bonds with the surface of glass or metal, resulting in a durable tough coating. By virtue of these advantages, the silane coupling agent is widely used as a coating agent to a variety of substrates.
As one typical example taking advantage of the above features, JP-A 58-167597 discloses a fluoroaminosilane compound of the following formula (3): ##STR1##
wherein R.sup.1 and R.sup.2 are C.sub.1-4 alkyl, Q is CH.sub.2 CH.sub.2 CH.sub.2 or CH.sub.2 CH.sub.2 NHCH.sub.2 CH.sub.2 CH.sub.2, m is an integer of 1 to 4, and n is equal to 2 or 3. However, this compound fails to take full advantage of the perfluoropolyether group because the perfluoropolyether moiety is as short as 2 to 5 monomeric units of hexafluoropropylene oxide (HFPO).
Also JP-A 58-122979 discloses a compound of the following formula (4) as a water and oil repellant applicable to a glass surface. ##STR2##
Herein, Rf is a polyfluoroalkyl group of 1 to 20 carbon atoms which may contain at least one ether bond, R.sup.1 is hydrogen or lower alkyl, A is alkylene, X is --CON(R.sup.2)--Q-- or --SO.sub.2 N(R.sup.2)--Q-- (wherein R.sup.2 is lower alkyl and Q is a divalent organic group), Z is lower alkyl, Y is halogen, alkoxy or R.sup.3 COO-- (wherein R.sup.3 is hydrogen or lower alkyl), n is an integer of 0 or 1, a is an integer of 1 to 3, and b is an integer of 0, 1 or 2. However, this compound is not satisfactory because the number of carbon atoms in the fluorinated group is as small as 1 to 20.
The present inventors previously proposed a perfluoropolyether of the following formula (5) in JP-A 11-29585. ##STR3##
Herein, X is a hydrolyzable group, R.sup.1 is lower alkyl, R.sup.2 is hydrogen or lower alkyl, Q is CH.sub.2 CH.sub.2 CH.sub.2 or CH.sub.2 CH.sub.2 NHCH.sub.2 CH.sub.2 CH.sub.2, m is an integer of 6 to 50, n is equal to 2 or 3, and x and y each are an integer of 1 to 3. Because of good water and oil repellency, anti-staining properties, chemical resistance, lubricity, and parting properties, this perfluoropolyether-modified aminosilane can be utilized as a surface treating agent by coating onto surfaces of various substrates. However, the compound is not regarded satisfactory in performance to form a coat because the content (wt %) of hydrolyzable groups per molecule is low and consequently, curing takes a time. In particular, since many tall buildings are constructed in the recent decades, the demand for the technology for imparting "stain resistance" or "ease of stain removal" for keeping glazing maintenance-free is increasing. There is a desire to have a material meeting such a demand.